For culturing Corynebacterium diphtheriae, the appropriate agar is:

Corynebacterium diphtheriae, the causative agent of diphtheria, requires specific growth conditions for effective culturing. Cystine-Tellurite agar is particularly well-suited for this purpose because it not only allows for the growth of C. diphtheriae but also helps in the differentiation of this organism. The tellurite in the medium reduces to tellurium, resulting in black colonies, which is a characteristic feature of C. diphtheriae and aids in its identification.

Blood agar does support the growth of many bacteria, including C. diphtheriae, but it does not provide the selective properties needed to distinguish this organism from other contaminating bacteria as effectively as Cystine-Tellurite agar does. MacConkey agar is selective for Gram-negative bacteria and would not support the growth of C. diphtheriae, which is Gram-positive. Egg yolk agar is primarily used for the cultivation of certain fastidious organisms and does not have the specific advantages of Cystine-Tellurite agar for culturing C. diphtheriae. Thus, Cystine-Tellurite agar is the most appropriate medium for the isolation and identification of this important pathogen.